1. Field of the Invention
The present invention relates to resin compositions comprising an ethylene-vinyl alcohol copolymer and a thermoplastic resin other than ethylene-vinyl alcohol copolymers and to methods for producing the same.
2. Description of the Related Art
Ethylene-vinyl alcohol copolymer, which may henceforth be abbreviated as EVOH, is a useful macromolecular material superior in oxygen barrier property, oil resistance, antistatic property and mechanical strength and is in wide use as various types of packaging materials such as films, sheets and containers. Although EVOH pellets are molded into various molded articles by various methods, they are often melt-molded by, for example, extrusion molding or injection molding. However, in general, when molding an EVOH resin, it is necessary to set the melting temperature to be 200° C. or higher. Therefore, EVOH containing no additives is liable to deteriorate when being melt molded and it accordingly may cause deterioration in product quality due to formation of fish eyes or hard spots in products. In addition, it is necessary to add some additives in order also to improve the interlayer adhesiveness when using it with other resins while laminating them.
In a pamphlet of WO 99/05213 (U.S. Pat. No. 6,174,949), disclosed is an EVOH resin composition containing a boron compound as an essential component, acetic acid as an optional component, and at least one compound as an essential component selected from among an acetic acid salt and a phosphoric acid compound, the content of each component based on 100 parts by weight of EVOH being 0.001 to 1 part by weight in terms of boron for the boron compound, 0 to 0.05 part by weight for acetic acid, 0.001 to 0.05 part by weight in terms of metal for the acetic acid salt, and 0.0005 to 0.05 part by weight in terms of phosphate group for the phosphoric acid compound. This resin composition is reported to be an EVOH resin composition having been improved in long-run workability, appearance and interlayer adhesiveness. The publication discloses that the purpose of the incorporation of the acetic acid salt is to improve the long-run workability or the interlayer adhesiveness.
JP-A-164059/2001 (EP-A-1090953) discloses an EVOH resin composition which is characterized in that, when it is heated to melt, its MFR shows specific behavior and that it contains from 50 to 500 ppm of carboxylic acid having a molecular weight of less than 75, from 50 to 500 ppm, in terms of metal element, of an alkali metal salt, from 10 to 120 ppm, in terms of metal element, of an alkaline earth metal salt, from 10 to 200 ppm, in terms of phosphate group, of a phosphoric acid compound and from 50 to 2000 ppm, in terms of boron element, of a boron compound. This resin composition is reported to be an EVOH resin composition which is superior in appearance and in long-run workability at the time of its melt molding, less suffers yellowing when being recovered, and shows a superior interlayer adhesiveness when being fabricated into a laminate. In this invention, the alkali metal salt and the boron compound are added for improving the interlayer adhesiveness and for improving the long-run workability, respectively.
As a typical method for producing pellets of an EVOH resin composition containing the additives, a method in which hydrous EVOH pellets are contacted with an aqueous solution containing the additives is disclosed. According to this method, it is easy to control the amounts of minor components contained in the EVOH resin composition pellets through an adjustment of the solution concentration and, therefore, it is possible to obtain pellets of stable quality by contacting them with the aqueous solution and then drying.
As mentioned above, the addition of an alkali metal salt to EVOH in order to improve the interlayer adhesiveness has been done conventionally. The alkali metal salt is added typically in the form of an acetic acid salt. In many cases, acetic acid, which is not in the form of a salt, is also added simultaneously. Such an EVOH resin composition containing an acetate group, however, may emit an acetic acid smell. One of the main applications of EVOH resin compositions is food packaging containers. In the market, EVOH resin compositions emitting smell as less as possible have been sought. In addition, EVOH resin compositions having a more improved melt stability and a superior long-run workability have been awaited.
On the other hand, in many cases where EVOH resin composition pellets are produced by contacting hydrous EVOH pellets with an aqueous solution containing acetic acid or its salt, acetic acid is released to the atmosphere when the hydrous pellets resulting from the contact are dried. Therefore, the surrounding environment and the working environment may be adversely affected.
A resin composition comprising an EVOH and a thermoplastic resin other than EVOHs are in wide use for improving the gas barrier property of the thermoplastic resin or for improving the flexibility, stretchability and flexing resistance of the EVOH as described below. In conventional production of such a resin composition, a method has been used in which a resin composition comprising an EVOH resin composition which was made contain additives by the method mentioned above is melt kneaded with a thermoplastic resin (G) other than EVOHs. Therefore, the problems with the above-mentioned conventional EVOH resin compositions have been left unsolved.
For example, resin compositions comprising EVOH and polyolefin are used widely for improving the gas barrier property of polyolefin or improving the flexibility of EVOH.
In addition, resin compositions comprising EVOH and polyamide are used widely for improving the gas barrier property of polyamide or for improving the flexibility of EVOH. For these purposes, use of a polyamide having a regulated amount of terminal amino groups as the polyamide is believed desirable. As resin compositions of a polyamide having a regulated amount of terminal amino groups and EVOH, various types of resin compositions have been proposed.
For example, there are known a technology of improving the melt moldability by use of a composition comprising an EVOH and a polyamide modified with monoamine compounds at its terminal carboxyl group (see, for example, JP-B-5-1819/U.S. Pat. No. 4,795,781) and a technology of improving the hot water resistance, the stretchability, and the like by use of a composition comprising an EVOH and a polyamide copolymer made up mainly of caproamide wherein the amount of terminal amino groups is regulated to be less than the amount of terminal carboxyl groups using a terminal regulating agent (see, for example, JP-A-4-178447). In addition, there have also been proposed a technology of improving the heat stability during melt molding by blending an EVOH with a polyamide whose terminal amino groups are modified to 30 μeq/g with acid anhydride, carboxylic acid and carboxylate (see, for example, JP-A-5-140386 and JP-A-4-114060), and a technology of improving the form retainability during or after retort sterilization in the case of forming a film or a multilayer packaging material by blending an EVOH with a polyaminde modified with a diamine compound and a carboxylic acid (see, for example, JP-A-8-259756).
EVOH is superior in transparency and gas barrier property, but it has drawbacks of being poor in stretchability, flexibility and flexing resistance. Known is a method of blending a flexible resin such as an ethylene-vinyl acetate copolymer and an ethylene-propylene copolymer to an EVOH to improve the defect. However, this method has a defect that transparency deteriorates greatly. As a substitute for these flexible resins, a pamphlet of WO02/092643 (EP-A-1403289) discloses a modified EVOH having an ethylene content of 5 to 55 mol % and containing 0.3 to 40 mol % of the following structural unit (I). This modified EVOH is superior in barrier property, transparency, stretchability, flexibility and flexing resistance and is used in the form of a mono- or multi-layer structure for various types of molded articles. The pamphlet discloses that the modified EVOH can also be used, for example, for coinjection blow molded containers, thermoformed articles and drawn film. It also discloses that that other resins or various types of filler may be blended with the modified EVOH.
wherein R1, R2, R3 and R4 each denote a hydrogen atom, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, an alicyclic hydrocarbon group having 3 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms; R1, R2, R3 and R4 may be the same group or may differ from each other; R3 and R4 may be combined together; and R1, R2, R3 and R4 each may have a hydroxyl group, a carboxyl group or a halogen atom.